WP Subtitle

The WP Subtitle plugin allows your pages and posts to contain a subtitle. Also called a sub-heading, this this short line of text is meant to appear beneath a post's (or page's) title, but can be inserted in your template wherever you choose.

<?php the_subtitle(); ?>

is used for inside The Loop. If you wish to get a page/post's subtitle outside The Loop, use <?php get_the_subtitle( $post ); ?>, where $post is a post object or ID ($post->ID).